The present invention relates to a receiving apparatus which receives, in an industrial process for example, a signal in the form of a current value and controls a control object device such as a valve.
In a typical industrial process, a receiving apparatus called a positioner is generally provided for remotely controlling valves, etc. In such a case, a signal in the form of a current value which changes in the range, for example, of 4-20 mA is transmitted from the central control unit. This signal is received by the receiving apparatus and controls devices in accordance with a current value.
However, the apparatus of the prior art has the disadvantage that a 2-wire system transmission line is required for transmission of a current value forming the signal and simultaneously another two wire system transmission line is required in order to supply the required power to the receiving apparatus. Namely, a 4-wire system transmission line is essential which increases the amount of wire material required for the transmission line and the man-hour effort required for wiring the system, and the facility cost also becomes high.
The prior art also has the disadvantage that an additional transmitting apparatus is required which must be connected with the control unit by an exclusive transmission line in order to monitor the control and operating conditions of valves, etc., and thereby an uneconomical investment is required.